Received April 09, 2009, in final form July 28, 2009; Published online August 04, 2009;
Misprints in Theorem B are corrected November 09, 2009

Abstract
Given a maximally non-integrable 2-distribution D on a 5-manifold M, it was discovered by P. Nurowski that one can naturally associate a
conformal structure [g]D of signature (2,3) on M. We
show that those conformal structures [g]D which come about by
this construction are characterized by the existence of a
normal conformal Killing 2-form which is locally decomposable and
satisfies a genericity condition. We further show that every
conformal Killing field of [g]D can be decomposed into
a symmetry of D and an almost Einstein scale of [g]D.